Reading object using fstream in C++

Question

I'm trying to use fstream to write an object to a file and read it after but when I try to show the object read on the screen using cout the error message Segmentation fault: 11 appears. Someone could help me with this code? Thanks in advance!

Produto *p1 = new Produto(1, "Refrigerante");

cout << "Produto p1 (pre serializacao): (" << p1->codigo << ") " << p1->descricao << endl;

ofstream serializationWriter;
serializationWriter.open("myobject.dat", ios::binary);
serializationWriter.write((char *)&p1, sizeof(p1));

Produto *p2;

ifstream serializationReader;
serializationReader.open("myobject.dat", ios::binary);
serializationReader.read((char *)&p2, sizeof(p2));

cout << "Produto p2 (pos serializacao): (" << p2->codigo << ") " << p2->descricao << endl;

use boost serialization! it is super awesome: boost.org/doc/libs/1_55_0/libs/serialization/doc/index.html — Fantastic Mr Fox
– Fantastic Mr Fox, Commented Jul 30, 2014 at 3:01
&p2 is a pointer to a pointer, a Produto**. You probably want to make p2 an instance as in Produto p2. — David G
– David G, Commented Jul 30, 2014 at 3:04
serializationWriter.write((char *)&p1, sizeof(p1)); The name of that variable is a misnomer. You are not "serializing" the data -- all you're doing is just taking a blob of bytes and writing it to a file. You don't serialize non-POD objects this way. — PaulMcKenzie
– PaulMcKenzie, Commented Jul 30, 2014 at 3:09
@PaulMcKenzie, it is worse. He's writing only a pointer to the file and reading the same numerical value of the pointer into p2 — R Sahu
– R Sahu, Commented Jul 30, 2014 at 3:26

vsoftco · Accepted Answer · 2014-07-30 11:50:49Z

2

You need provide some serialization mechanism for class Produto. For example:

class Produto {
  // ...
private: 
  std::string m_str;
private: 
  friend ostream& operator<<(ostream& stream, const Produto& obj);
  friend istream& operator>>(istream& stream, Prodoto& obj)
};

ostream& operator<<(ostream& stream, const Produto& obj)
{
  // Write all data to stream.
  // ...
  stream << obj.m_str;
  return stream;
}

istream& operator>>(istream& stream, Prodoto& obj)
{
  // Read all data from strem.
  // ...
  stream >> obj.m_str;
  return stream; 
}

And then use it as below:

Produto p1(1, "Refrigerante");
ofstream serializationWriter;
// ...
serializationWriter << p1;

Produto p2;
ifstream serializationReader;
// ...
serializationReader >> p2;

For more details see overload ostream istream operator

edited Jul 30, 2014 at 11:50

vsoftco

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answered Jul 30, 2014 at 3:19

PSyton

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